Touch screens are used in many portable electronic devices, for instance in PDA (Personal Digital Assistant) devices, tabletops, and mobile devices. Touch screens are operable by a pointing device (or stylus) and/or by finger. Typically the devices also comprise conventional buttons for certain operations.
Three dimensional (3D) content display techniques and 3D interaction, or sense of 3D interaction, have been under development also for portable electronic devices. It has been suggested to apply also the space above a touch screen surface as further means for user inputs. People who are using mobile devices generally wish to have more versatile and intuitive ways to interact with their devices.